Anode power supply



May 30, 1944. w Ts 2,350,206

ANODE POWER SUPPLY Filed Oct. 14, 1942 Inventor; Ddnald ElWacts,

His Attonney.

Patented May 30, 1944 ANODE POWER SUPPLY Donald E. Watts, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application October 14, 1942, Serial No. 461,945

4 Claims.

My invention relates to radio transmitting equipment and particularly to dynamo-electric generators supplying operating potential for the electron tubes of such equipment. It is an object of my invention to eliminate the instability of such transmitting equipment caused by overcompounding of the generators.

In radio transmitting equipment, it is well known to use, in dynamo-electric generators supplying operating potentials to the anodes of the amplifiers of the equipment, a rotor carrying two similar windings and two commutators, and to supply to difierent stages of the amplifier the potential developed in one or both of the windings, depending on the requirements of aparticular stage. It is customary also to use both series and shunt field windings in such generators to obtain adesired voltage characteristic at normal anode voltage on the amplifier tubes. As a result the anode current in one stage affects the anode voltage, and the anode current, in the other stages.

It is found in the use of such a potential source that, when the equipment is operated at reduced anode voltages on the stages of the transmitter, detuning of the power amplifier causes the anode voltage to rise very rapidly, indicating an unstable condition. Similarly, whenever the final power amplifier plate current exceeds a certain value, dependingon the frequency and the amount of excitation, the anode voltage on the stages operating from the same generator rises very rapidly. With the power amplifier detuned, most of thepower is dissipated on the anodes of the amplifier tubes, endangering their operation. Moreover, protection for the tubes under such conditions is not provided by the customary overload relay because the anode current does not reach a high enough value at such reduced voltage to trip the relay.

' The above described instability may be attributed to a combination of two factors, namely, high overcompounding of the high voltage anode generator present at reduced voltages of the order of 75% to 40% of full load volta e and the fact that, when the anode voltage rises, excitation is automatically increased on the power amplifier tubes causing them to draw more anode current. This cycle is repeated many times until ultimately the anode voltage reaches some maximum value.

, Such instability may be eliminated by pro- .viding a separate generator for the tubes of the power amplifier stage. .Such a system is costly and increases greatly the weight andspace requirements of the transmitter. Again the instability may be reduced by elimination of the series field of the generator. Such a change, however, increases, undesirably, the regulation of the generator at full load voltage. It is an object of my invention to provide means for reducing such instability by decreasing the amount of series field excitation as the anode voltages of the power amplifier and preceding stages are decreased.

The features of my invention which I believe to be novel are set forth with particularity in the appended claims. My invention itself, however, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in which the single figure illustrates a potential source embodying my invention for the power amplifier stages of a radio transmitter.

Referring to the drawing, the portion of the radio transmitter shown comprises the intermediate power amplifier stages l0 and II, the final power amplifier stage l2, requiring different anode potentials for the electron discharge devices of these stages, and th potential source l3 for supplying a stable, adjustable anode potential to these amplifier stages.

In the portion of the transmitter circuit shown, the intermediate power amplifier l0 amplifies radio frequency signal supplied to its control electrode H from the preceding transmitter equipment, not shown, and which includes a controlled source of radio frequency oscillation, and which may include a source of audio frequency signal and means for modulating the radio frequency signal. It will be apparent that the stage I0 may also be a frequency multiplying stage. The tuned output circuit l5 of amplifier I0 is coupled by means of capacito Hi to the control electrode ll of intermediate power amplifier H. Similar to amplifier ID, the tuned output circuit I 8 of amplifier II is coupled by means of capacitor l9 to control electrode 20 of the final power amplifier l2 and the tuned output circuit 2| of amplifier I2 is connected by conductor 22 to any suitable output means, for example an antenna, not shown.

The amplifiers of these stages to and II are shown as of the pentode type having the conventional screen electrodes 26 and suppressor grids 21. Also the inductances 28 in the control electrode biasing circuits of the stages l0l2 act as the usual radio frequency choke coils. The amplifier of stage 12 is shown as a triode employing the neutralizing capacitor 29 to prevent feed back of voltage from the tuned output circuit 2| to the control electrode 23.

Potential source I3 comprises the rotor member 33 having two similar armature windings, not shown, connected respectively to commutators 3i and 32, excitation for the armature windings being supplied by the shunt field winding 33 and the series field winding 34. The rotor 30 is rotated at a constant speed by any suitable means, such as the direct current motor 35. The shunt, or main, field winding 33 may either be self-excited or, especially in the case of high voltage generators, separately excited by connection to a source of unidirectional potential, such as the battery 35. Series field winding 34 preferably is connected between the negative brush on commutator 31 andground. The

positive brush on commutator 3! is connected to the negative brush on commutator 32 by means of conduct-or 31-.

From the potential source l3, anode potential of one value is supplied to the anodes of amplifiers' l9 and H through tuned circuits l5 and I8 and conductor 31. Inductances 23 and 2-3 are provided in these connections to eliminate any radio frequency. currents present therein to prevent'their appearance on conductor 31.. The higher voltage required for the anode of plate amplifier I2 is obtained by connecting the tuned circuit 21 to the positive brush on commutator 32-, the inductance 25 being included in this circuit-to eliminate any radio frequency, if present, from feeding-back to the voltage supply 13. It will-readily be apparentthat the voltage supplied to the anode of amplifier i2 is the sum of the voltages-generated in the two armature windings onrotor member 30,'the magnitude of the output voltages of the two armature windings beingdetermined, for reasons well known, by the magnitude of the current in the shunt field winding 33. Also, in the above-described dynamo electric generator', comprising the rotor member 30 and the field windings 33 and 34, the regulation of the generator at full load voltage isdetermined by the strength of the series field.

In the operation of radio transmitting equipment using the above described power amplifier circuit with the-anode voltage supply thus far described, it has been observed that when the transmitteris operated at reduced plate voltages on the intermediate power amplifier and power amplifier stages Ill-42, detum'ng of the power amplifier circuit causes the anode voltages on these stages to rise very rapidly, indicating an unstable condition. Similarly, when the anode current'of the power amplifier exceeds a certain value, depending on the carrier wave frequency and the amount of excitation, unstable anode voltage conditions are likewise observed. As is well known to those skilled in the operation of power amplifiers, the power that the anode supply voltage must furnish to the tube is equal to the product of the anode voltage and the anode current under any conditions. Consequently, when the power amplifier circuit 2i is detuned and the above-described unstable condition occurs, most of the power is dissipated on the anodes of these tubes, and appears as heat that must be radiated, thus endangering their future operation. Protection from an overload relay is notpossible under such conditions since the anode current does not rise high enough at the reduced voltage being applied to the tube to trip the relay.

The above-described unstable condition may be attributed to a combination of high overcompounding of the generator of the anode voltage supply I3, which occurs when the machine is operating at reduced voltages, and also to the fact that when the anode voltage rises, excitation is automatically increased in the amplifier tubes l,lll2, causing the power amplifier. to draw more plate anode current. Thiscycle is continued again and again until the anode voltage reaches some maximum value.

In accordance with my invention, the instability of such a machine is reduced by providing the variable resistance 38 in shunt with the series field 34 for bypassing. some of the series field current and by adjusting the amount of resistance so shunted across the series field 34 simultaneously with adjustment of the resistance 39 in series with shunt field 33 for controlling the amount of shunt field excitation. As shown, both resistances 38 and 39 have respectively the arms, or contact making members, All and M making contact with variable points onthe respective resistances and linked together mechanically for simultaneous operation, With the arms 40 and. 4| so. mechanically linked, it will beseen that, as the value of resistance in series with shunt field 3.3. is increased in order to decrease the value of the anode voltage, the value of the resistance shunted across series field 34 is decreasedso that the resistance 38 bypasses a greater portion of the, series field current. Preferably, the resistance 3.8 does not vary uniformly with changes in the angular position of the arm 4i], butdecreases rapidly in value as the plate voltage is reduced by increase of the resistance 39,. Thus, for lower values of anode voltage, the resistance 38is. ffective ,to bypass practically all of the current of-the, series field 3 making the output voltage of the generator less respqnsiveto variation in the anode current of. the amplifier tubes. Also, as a resultof the non-linearity of resistance 38 this resistance .is ofvery h h value as. rated anode voltage is approached and becomes. discontinuousvw'nen the point 42 is reached, automatically assuring the required amount of re ulatiQn r the enera or atfull load volta e.

In order to facilitate tnning'of the. transmitter, adjustable resistor '43 is. Provided in, series with resistance 3:9 andswitch. 44. is providedjforin- Also, in order to eliminate the previously men= tioned instability causedby the. presenceof. series fijeld 3.4 at, low values of anode potential, switch 45 provided to shortecircuit.resistance. 38v and ser es field-34 during a tuning: period, switches. 44 and 45 being mechanically interlinked rorgang operation. A thirdcontact. position 3 is provided on bothswitches 4.4:and 45. for removingpotem tial from the anodes of: the power amplifier. and intermediate power amplifier tubes. shown.

It will thus be seen that my inventionv provides an anode power supply in which; instability, due to overcompounding oi'the anode generator, is eliminated by shuntingtheseries. field coil. of

the generator. with ayresistance to bypass. the

ing means for adjusting the value of this resistance simultaneously with adjustment of the value of anode potential to bypass the desired amount of field current for a particular voltage setting. of course, it will be apparent that in particular installations it may be desirable to connect this resistance across a part of the series field only, rather than the entire field, in order to obtain the proper operating characteristics. Further, my invention provides means for easily tuning the transmitter and for short-circuiting the series field during such tuning operation to obtain fairly fiat compounding of the generator.

While I have shown a particular embodiment of my invention, it will of course be understood that I do not wish to be limited thereto since various modifications may be made, and I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a unidirectional potential source for a plurality of stages of electron discharge devices operating at difierent variable potentials and adversely affected by fluctuations in operating potential, the combination of a dynamo electric machine having output terminals supplying said potentials to said stages, a series field winding and a shunt field winding, first and second adjustable resistances connected respectively across said series field winding and in series with said shunt field winding, means for adjusting said resistances simultaneously in opposite sense, said adjustment of said first resistance being effective to provide a stable operating characteristic for said machine as the potential of said machine is varied over a wide range by said adjustment of said second resistance, and means for adjusting said potential to a desired value to facilitate tuning said stages, said last means comprising means for short-circuiting said series field and inserting a second adjustable resistor in series with said shunt field.

2. A unidirectional potential source for a plurality of amplifiers operating at different variable potentials comprising, a rotor member having a pair of similar windings, one of said windings being connected to one of said amplifiers, and

both of said windings in series being connected to another of said amplifiers, a shunt field winding having an adjustable resistance in series therewith, a series field winding having an adjustable resistance in shunt thereto, and. means for adjusting said resistances simultaneously in unlike sense to reduce the excitation of said series field winding as the potential supplied to said another amplifier is decreased.

3. In a direct current generator for supplying power to a radio transmitter having a plurality of stages of amplifiers operating at different variable potentials, the combination of a rotor member having a pair of series connected windings and a commutator for each winding, means connecting one of said windings to one of said stages, means connecting both of said windings in series to another of said stages, shunt and series field windings associated with said memher, a pair of adjustable resistances connected respectively in series with said shunt field and in shunt to said series field, said resistances being adjustable simultaneously in opposite sense to reduce the excitation of said series field winding as the potential supplied to said another stage is decreased, and means to short-circuit said series field and to provide a predetermined potential to facilitate tuning said transmitter.

4. In combination, a plurality of stages of amplifiers operating at difierent potentials and adversely affected by fluctuations in operating potential, a source of operating potential therefor comprising, a rotor member having a pair of series connected windings connected respectively to different stages of said amplifier, shunt and series field windings associated therewith, an adjustable resistance connected in series with said shunt field winding, means for preventing fluctuations in sa d potential comprising, an adjustable resistance connected across said series field winding, means for simultaneously adjusting the magnitudes of said resistances in opposite sense, and means for adjusting said potential to a desired value to facilitate tuning said stages, said last means comprising, means for short-circuiting said series field and inserting a second adjustable resistor in series with said shunt field.

DONALD E. WATTS. 

